Member for measuring a common mode voltage in an electrical network and device for detecting a fault using such a member

ABSTRACT

A member for measuring a variable representative of a common mode voltage in an electrical network a device. The network or the device includes at least a first power conductor and a second power conductor. The measuring member has two capacitive elements which are intended to be arranged in a bridge between the two power conductors and have capacity values that are identical to each other. The two capacitive elements are connected at a midpoint. The measuring member also includes a two-terminal measurement circuit connected on the one hand to the midpoint and on the other hand to a connection terminal intended to be electrically connected to a common conductor provided in the electrical network or device.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and a method for detecting afault in an electrical energy distribution network. It also concerns anelectrical energy distribution network or an equipment equipped withsuch a detection device.

TECHNICAL BACKGROUND OF THE INVENTION

The needs to reduce the carbon footprint of the human activity, as wellas the need to optimize the energy efficiency, leads to the use of theelectrical energy. This job requires to convey the electrical energy, ina direct (DC) or alternating (AC) form, between one or more sources (abattery, a generator, photovoltaic panels for example) and one or moreloads (electric motors, inverters, etc.) by means of distribution lines,protection systems (circuit breaker, disconnecting switch, and otherbreaking members). The set of sources, loads, lines and protectionsystems constitutes the electrical network.

The network is sometimes required to convey large amounts of power thatcan exceed several tens of kilowatts, even hundreds of kilowatts, oreven megawatts. It can be embarked in a vehicle such as a land vehicle(car or tank) or railroad, a surface ship or a submarine or an aircraftfor example. It is therefore likely to operate in a severe environment,i.e. one that can present large amplitudes of temperature, pressure,vibration, electromagnetic fields or humidity. A fault of the network inthese applications can have serious consequences, so it is imperative tosecure it.

More generally, and independently of the field of application, it isimportant to be able to detect, and advantageously to localize, a faultoccurring in an electrical network. A network is usually protected bymeans of protection devices, with the detection of a fault leading tothe switching of these devices to electrically isolate at least aportion of the network. These can be, for example, circuit breakers,contactors, solid state switches, fuses or current limiters that switchon when excessive currents occur. The localization of a fault allowsonly the faulty section of the network to be isolated, and thisfunctionality is advantageous in that it allows a minimum operationlevel of the network to be maintained as well as a targeted interventionby a maintenance team.

The faults that can occur in an electrical network are of variousnatures: insulation defects, losses by excessive switching at the levelof a load, excessive energy consumption, short-circuit, etc. It can alsobe the formation of an electric arc in, or between, the conductors thatmake up the distribution lines and the electrical apparatus. An electricarc corresponds to an unintentional discharge propagating in a gas (air)between two conductive segments of the network. When such a dischargeoccurs in an electrical insulator encasing a conductor withoutcompletely damaging it, it is referred to as “partial discharge”. Theseelectrical discharges can be caused by many things, such as improperconnection of the conductors, the degradation of the electricalinsulator surrounding these conductors, the presence of foreign objectsor the poor quality of an insulator. They are frequent phenomena in thenetworks and are likely to cause fires, explosions, phenomenal localtemperature rises of over 10,000° C., high overpressures and theemission of significant ultraviolet radiation. The appearance of theseelectrical arcs is favoured by humidity, depression and temperature ofthe environment so that their early detection is particularly essentialwhen the network operates in a severe environment as mentioned above.

The electrical arcs are usually not detected early enough by the usualprotection devices, such as circuit breaker, which are triggered on thebasis of an excessive current or power consumption. Some electrical arcsdevelop over very long periods of time, without causing the appearanceof overcurrent or overpower in the network that would allow their earlydetection by the usual means. This is in particular the case for“series” arcs that can develop in a power conductor or in a connector.The power dissipated during the start-up of a series arc is much lowerthan that of a parallel arc or the nominal power of the network.

The detection of the electrical arcs in a network is generally carriedout by monitoring the temporal and/or frequency evolution of the signalsof the network (current and/or voltage), knowing that the occurrence ofsuch a phenomenon leads to the formation of signals with a strongspectral content, even in the case of a direct network. An example ofsuch a detection solution is in particular presented in the documentU.S. Ser. No. 10/078,105. However, these methods based on the temporalor spectral analysis of the signals, current and/or voltage, areparticularly difficult to implement and lead to many false positives,which can be caused by the loads or the active sources (i.e. switched)present on the network. In particular, they are not efficient indetecting the occurrence of a series electrical arc in a direct network(DC).

OBJECT OF THE INVENTION

An aim of the invention is to remedy the aforementioned disadvantages.One aim of the invention is in particular to propose a device and amethod for detecting faults in an electrical network which areparticularly reliable and which are adapted to detect the occurrence,and advantageously to localize, a wide variety of faults, includingelectrical arcs and in particular series arcs, in particular in a directnetwork.

BRIEF DESCRIPTION OF THE INVENTION

With a view to achieving this aim, the object of the invention proposesa member for measuring a quantity representative of a common modevoltage in an electrical network or in equipment, the network or theequipment comprising at least a first power conductor and a second powerconductor, the measuring member comprising two capacitive elementsintended which are intended to be arranged in a bridge between the twopower conductors and having capacitance values that are identical toeach other, the two capacitive elements being connected at a mid-point.The measuring member further comprises a measuring dipole connected onthe one hand to the midpoint and on the other hand to a connectionterminal intended to be electrically connected to a common conductor ofwhich the electrical network or the equipment has been equipped.

According to other advantageous and non-limiting characteristics of theinvention, taken alone or in any technically feasible combination:

-   -   the measuring dipole has an impedance of less than 1 kOhms, the        dipole being able to develop a voltage proportional to the        derivative with respect to time of a common mode voltage present        between the two power conductors;    -   the measuring dipole has an impedance greater than 1 kOhms, the        dipole developing a voltage proportional to a common mode        voltage present between the two power conductors;    -   the capacitive elements are formed by a three-terminal        capacitor, a first terminal being intended to be electrically        connected to one of the power conductors, a second terminal        being intended to be electrically connected to the other of the        power conductors and the third terminal being intended to be        connected to the common conductor;    -   the three-terminal capacitor is made of only 3 electrodes;    -   the three-terminal capacitor is made of sheets stacked and then        rolled up to form a cylinder or a 3-terminal parallelepiped;    -   the measuring member further comprises a three-electrode        resistor having a midpoint, the first electrode being intended        to be electrically connected to the first power conductor, the        second electrode being intended to be electrically connected to        the second power conductor, the common mode voltage being        present between the midpoint of the three-electrode resistor and        the common conductor.    -   the measuring member comprises a current sensor, capable of        measuring the differential mode current flowing in the two        capacitive elements, in order to establish a quantity        representative of the common mode voltage, and formed by at        least four air coils respectively arranged in the vicinity of        the capacitive elements;    -   the measuring member further comprises a current sensor, capable        of measuring the common mode current flowing in the two        capacitive elements in order to establish a quantity        representative of a differential mode voltage;    -   the current sensor for measuring the common mode current is        formed by at least two air coils respectively arranged in the        vicinity of the capacitive elements;    -   the measuring member further comprises a sensor for the DC        component of the common mode voltage (V_(res));    -   the measuring member further comprises a sensor of the DC        component of the differential mode voltage.

According to another aspect, the invention provides a device fordetecting a fault in an electrical network, the electrical networkcomprising at least one electrical equipment electrically connected to afirst power conductor and a second power conductor. According to theinvention, the network also being provided with a common conductor, thedevice being intended to be connected to the power conductors and thecommon conductor at a measuring area and comprising:

-   -   a first measuring member as described above;    -   a second measuring member for producing a second quantity        representative of a network current flowing through the power        conductors;    -   a calculator, connected to the first and second measuring        members, the calculator being configured to determine, over a        determined observation period, a quantity representative of a        so-called “mixed” energy defined as the integral over the        determined observation period of the product of the common mode        voltage and the network current and conveyed in the measurement        area, the quantity representative of the mixed energy being        determined from the first quantity and the second quantity.

According to further advantageous and non-limiting characteristics ofthis aspect of the invention, taken alone or in any technically feasiblecombination:

-   -   the second measuring member comprises an air coil, for example        of the Rogowski type;    -   the second measuring member also comprises a direct current        sensor, for example a Neel Effect® sensor.

BRIEF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the invention will be apparentfrom the following detailed description of the invention with referenceto the attached figures, in which:

FIGS. 1 a and 1 b show examples of an electrical network according toone embodiment of the invention;

FIG. 2 represents the state of the network at a time of an observationperiod j established by a supervision device;

FIG. 3 illustrates a section of an electrical network according to theinvention;

FIGS. 4 a, 4 b and 4 c show respectively a network section during theoccurrence of a parallel type, insulation defect type and series typefault;

FIG. 5 shows a detection device according to one embodiment of theinvention.

FIG. 6 represents a schematic circuit forming another embodiment of afirst measuring member of a detection device.

FIG. 7 represents an example of the embodiment of a first measuringmember of a detection device;

FIGS. 8 a and 8 b represent another example of the embodiment of a firstmeasuring member of a detection device;

FIG. 9 represent a system for detecting and localizing a fault inaccordance with the invention.

FIGS. 10 and 11 show preferred embodiment examples of a sensor for ameasuring member compatible with a detection device of the invention.

DETAILED DESCRIPTION OF THE INVENTION

For the sake of simplicity of writing, we will assimilate in the presentdescription a quantity (an energy, a voltage, a current for example)with the measurement of this quantity (the quantity representing themeasured or estimated energy, voltage or current).

Electrical Network

FIGS. 1 a and 1 b show two examples of an electrical network 1 whoseproper operation is to be monitored, by detecting the occurrence of itsfaults and, advantageously, by localizing them. These faults, aspresented in the introduction of this application, can be of verydiverse natures, a series or parallel electric arc, an overconsumption,a short-circuit or any other insulation defect.

In a conventional way, this electrical network 1 comprises at least twopower conductors that allow the required power to be transited. Theelectrical network 1 can be a direct network (DC), and it will then beconsidered that it has a network frequency between zero and 5 Hz to keepall its generality to the present description. This can be afixed-frequency conventional single-phase alternating network with anetwork frequency of 50 Hz or 60 Hz or 400 Hz plus or minus 5 Hz, or avariable-frequency alternating network, typically between 360 and 800Hz. But more generally, the electrical network 1 can operate in anysuitable frequency range. The present invention is also applicable tothe multiphase networks, such as a three-phase network for example.

The invention is particularly applicable when the electrical network 1is aimed to convey a relatively large amounts of power between thevarious electrical equipment, sources or loads, which make it up.Preferably, therefore, the voltages and currents developing on theelectrical network 1 have values typically higher than, respectively,50V, 330V, 600V, 1000V, 3000V or 10000V and 100 A. But nothing excludesthe application of the principles of the invention to electricalnetworks conveying relatively smaller powers.

As can be seen in FIG. 1 , the electrical network 1 comprises aplurality of electrical equipment E (and more generally, at least oneelectrical equipment E), sources or loads, and conductive lines Lconnecting some of the equipment E to each other, here in the form of ameshed network, so as to electrically feed the loads with the energysupplied by the sources. The electrical equipment E are connected to thelines L by means of connection terminals B. The protection members, suchas circuit breaker, disconnectors or any other breaking member, are partof the network 1 and its electrical equipment E even if they are notshown in the figures.

The electrical equipment E can be of any kind that is suitable for thefield of application of the network. Some of these equipment E canalternatively form a source and a load (generator/motor). It can be apower distribution equipment. The equipment can be active, such as aninverter, or passive. The electrical equipment E, when they formsources, can be for example batteries or generators or photovoltaicpanels or wind turbines, etc. There can be a combination of severalsources and several loads in the same network. In FIG. 1 b , we haverepresented a distribution equipment E1 arranged at the level of a nodeof the network between a source Es, and two loads arranged at the end oflines L.

In order to allow the protection of the network 1, it is equipped with acommon conductor (which will be described in more detail in a latersection of this description) and it contains at least one detectiondevice D and advantageously a plurality of such devices D distributed inthe network 1 at the level of a plurality of measurement areas. Adetection device D has connection terminals allowing to connect it tothe conductors of the lines L or of the equipment E, in order to placeit effectively in the network. Preferably, the detection device D isnon-intrusive, i.e. it is connected in parallel to the power conductorsof the lines L and to the equipment E forming the network 1 (for examplefor the voltage measurements), or it implements non-intrusive sensors(for example of the air coil, Hall effect or Neel Effect® type for thecurrent measurement). This reduces the number of interconnections on theconductors and thus the risk of arc-type faults.

The invention provides for a distinction to be made in all the energyconveyed by the network, and therefore at the level of each measurementarea, between an energy referred to as “energy of network”, an energyreferred to as “residual energy” and an energy referred to as “mixedenergy”. The network energy corresponds to the energy conveyed in ameasurement area when the network is perfectly balanced and in theabsence of any fault. The residual energy and the mixed energy reflectan imbalance in the electrical network 1 that occurs and is caused bythe occurrence of a network fault. However, the residual and mixedenergies are not completely zero in a healthy network, due to certainnatural imbalances. For this reason, according to some embodiments ofthe invention, it is foreseen to measure point-to-point differences ordifferences in distinct instants between energies in order to detect,and also to localize, certain faults without generating false-positiveslinked to natural imbalances.

As will be detailed in a later portion of this description, a detectiondevice D in accordance with an embodiment of the invention is adapted tomeasure the network energy E_(net), the residual energy E_(res) and themixed energy E_(mix), transiting at the level of the measurement area ofthe network 1 in which it is localized, and during successiveobservation periods. The measurement of these energies allows to detectand sometimes to localize the occurrence of a fault in the network 1 orin a section of the network 1. At least, such a detection device D isadapted to measure a mixed energy E_(mix) so as to allow the detectionof a series arc. For the sake of clarity, we specify that by “localizinga fault”, we mean the ability to identify the section of the electricalnetwork 1 or to identify the equipment E in which the fault hasoccurred. This section can be defined by the portion of the networkcomprised between two detection devices D, or by a source type equipmentE arranged upstream of a device D, or by a load type equipment Earranged downstream of a detection device D.

The electrical network 1 may also comprise a protection device P, or aplurality of such devices P, allowing to isolate a section of thenetwork 1, such as a line L or an electrical equipment E. These may beconventional circuit breakers for example. In general, such devices Pare placed either at the level of a source, at the level of a load, or,most often, at the level of the nodes of the network via distributionequipment E1, as shown in FIG. 1 b.

The detection devices D and the protection devices P can be distributedvery freely in the network 1, according to its nature and its topology,in order to ensure its protection. These devices D, P can be placed oneand/or the other at the end of a line L, on a section of line L orintegrated in an electrical equipment E. A detection D and protection Pdevice are not necessarily associated with each other, although it canbe advantageous in some cases to associate them, for example in the samecase, so as to realize a single module allowing to implement the twofunctions of detection and protection. In this case, a detectionterminal of the detection device D, over which a detection signal S isgenerated when a fault is detected, can be connected to a triggerterminal of the protection device P.

Some sections of the network 1, lines L or equipment E, may not beequipped with detection devices D and/or protection devices P. In thiscase, it may not be possible to detect or localize the occurrence of afault in this section of network 1 and/or to disconnect this section ofthe network 1. However, it may be possible to detect the occurrence ofthe fault from a detection device D arranged outside the occurrencesection of the fault and to protect the network 1 as a whole, forexample by disconnecting it from the equipment E forming the energysources. To do this, and as will be presented in detail in the rest ofthis presentation, we can measure energy variations directly at theoutput of a source or directly at the input of a load. When a detectiondevice D is placed at the source output, respectively load input, it ispreferable to place it as far upstream as possible, and respectively asfar downstream as possible, so that defects can also be detected in theprotection devices P or the connection terminals B.

As will become apparent in the rest of this description, some categoriesof faults are detectable locally, in a measurement area, from the solemeasurements of the network energies E_(net), residual E_(res) and/ormixed E_(mix) carried out in this area. This is in particular the casefor a series arc, an insulation defect or an overconsumption. Thedetection device D is then adapted to generate an electrical signal S,on a detection terminal of this device D, indicating the occurrence of afault of the network 1. When the detection device D is locallyassociated with a protection device P, this signal S can be locallyexploited by the protection device P to immediately isolate the sectionof the faulty network, line L or equipment E, from the rest of thenetwork 1.

To detect other categories of faults, such as the occurrence of anelectric arc between two parallel conductors, to localize faults in thenetwork 1 more precisely, or to qualify a fault in terms of energyconsumed, it may sometimes be necessary to exploit the energymeasurements E_(net), E_(res), E_(mix) supplied by a plurality ofdetection devices D. To this end, and according to a particularembodiment of the invention, it is provided to associate with theelectrical network 1 a supervision device V. This device V, typicallyimplemented by a digital calculation member, is connected to at leastsome of the detection devices D of the network 1 by means of acommunication bus BUS, represented in dotted line on FIG. 1 . Any typeof bus can be suitable for implementing the communication bus BUS,including in particular a serial bus or a parallel bus operating underany possible form of protocol, whether it meets an established standardor not. It should be noted that the supervision device V can beintegrated into one of the detection devices D. In this case, it can beprovided that these devices D comprise a calculation member making themadapted to implement the supervision processing, at least one of thesedevices being then activated to operate as the supervision device V ofthe network 1.

In a configuration in which the network is equipped with a plurality ofdetection devices D coupled to a supervision device V, these devices areconfigured to place on the communication bus BUS data indicating theoccurrence of a fault and/or data representative of the energiesE_(net), E_(res), E_(mix) which they measure over a given observationperiod. The detection devices D are identified, on the computer networkformed by the communication bus BUS, by means of a unique identifier.The communication bus BUS comprises a clock information distributed tothe various detection devices D so that they share a common time base.The data E^(j) _(net,i), E^(j) _(res,i), E^(j) _(mix,i) representativeof the energies measured by an identifier device i and placed on thecommunication bus BUS during a determined observation period j can thusbe ordered and processed by the supervision device V to determine thestate of the network at a given moment, i.e. the network, residual,mixed energies that transit in each measurement area during a givenobservation period.

FIG. 2 shows the state of the network 1 of FIG. 1 at an instant of anobservation period j as it can be established by the supervision deviceV. Each detector of the network D1, D2, D3, D4 is identified here by anindex corresponding in a simplified way to its identifier on thecomputer network. Each detector places its mixed energy measurementE^(j) _(mix,i) (and its other measurements E^(j) _(net,i), E^(j)_(res,i) not shown on FIG. 2 ) on the communication bus BUS, whichallows the supervision device V to inform a data structure of the stateof the network, symbolized on this FIG. 2 by tables T of the energylevels which transit in each measurement area. This data structure canrecord, in a table indexed by the observation period j, the network,residual and mixed energies of each measurement area. Detection devicesD (not shown in FIG. 2 ) can advantageously be placed at the level ofdistribution “nodes”, for example in distribution equipment of thenetwork 1, as shown in FIG. 1 b.

The supervision device V is configured to exploit the data supplied bythe detection devices D of the network 1 and delivered by thecommunication bus BUS. The purpose of this exploitation is to detect afault of the network and/or to localize this fault in the network 1and/or to qualify, in terms of energy, a detected fault.

The supervision device V can emit a signal indicating the fault of thenetwork 1 and this signal can be exploited to disconnect a section ofthe network. For this purpose, the supervision device V can be connectedto at least some of the protection devices P of the electrical network 1in order to activate them, where appropriate. This can be apoint-to-point connection or a connection implementing the communicationbus BUS, or another dedicated bus, to which the protection devices P arethen connected. In another embodiment, the supervision device, inparticular when it is integrated in one of the detectors D of thenetwork, can communicate with a third-party device responsible forcontrolling the protection devices P of the network.

It is thus understood that according to the embodiment of the inventionrepresented in FIGS. 1 a and 1 b , there is an electrical network 1 anda plurality of detection devices D distributed on the network 1 at thelevel of measurement areas, these devices D communicating to asupervision device V of the data E^(j) _(net,i), E^(j) _(res,i), E^(j)_(mix,i) representative of energies which transit in these measurementareas i during a determined observation time period j. The supervisiondevice V can exploit this data to represent the state of the network,i.e. the energy that transits in each measurement area during successiveobservation periods.

An energy data, or a data representing a variation of energy higher thana certain threshold allows to detect a fault without necessarily beingable to localize it (except at the level of the ends of the networkwhere a variation of energy can allow to localize a defect). On theother hand, the analysis of the differences in energies that transitbetween two (or more) detection devices D allows not only to improve thequality of the detection, but also to localize a fault between these twodetection devices (D). To this end, the supervision device V can beconfigured to exploit the information supplied by the detection devicesD on the communication bus BUS to localize a fault occurring in theelectrical network 1 in the section of the conductors C1, C2, Ccincluded between these two devices or in an equipment E of the network.A system for localizing a fault in the network is thus available, asshown in FIG. 9 , by equipping it with at least two detection devices D.

The supervision device V is therefore adapted to detect and/or localizeand/or quantify the occurrence of a fault on the electrical network 1 inorder to protect it, for example by disconnecting the section of thenetwork 1 in which the fault has been localized.

Common Conductor

In order to allow the distinction between the different forms of energyconveyed by the network 1 formed by the power conductors on which theenergy transits, the invention provides for the network 1 to be equippedwith a common conductor. This common conductor forms a reference voltagefor all electrical equipment E in the network to which it iselectrically connected. It can be a mechanical mass of the network, or aneutral, but it is not necessarily the case. The common conductor is notintended to carry an intense current, but it may be at a high potentialrelative to the mechanical mass. It can be a simple telecommunicationcable, for example a cable constituting, at least partly, thecommunication bus BUS described above. Alternatively, it may be aconductor similar to those forming the power conductors. The commonconductor can be connected to a midpoint connection terminal of the“source” or “load” type equipment E when these are symmetrical (e.g. twomidpoint batteries or the midpoint of an inverter or the midpoint ofphotovoltaic panels). The common conductor can be connected to anexisting midpoint of an equipment, source or load, or to a“manufactured” midpoint from a resistive divider on the source and/orload side. This dividing bridge allowing for connecting the commonconductor can be integrated into a detection device D.

In the case of a bipolar configuration (single-phase alternating AC ordirect DC network), a line L is therefore made up of a first and asecond power conductor to which a common conductor is added. In the caseof a three-phase configuration, a line L comprises a third powerconductor and the common can be connected to the neutral. For the sakeof simplicity, we will consider in the following that the network 1 is abipolar network comprising two power conductors to which a commonconductor is added, but the principles described apply generally to anetwork comprising any number of power conductors.

Definition of the Network, Residual and Mixed Energies

To illustrate the benefit of the common conductor in the scope of thedetection of a fault in an electrical network, FIG. 3 shows, by way ofillustration, a section of an electrical network comprising a line Larranged between a source S and a load C. The line L is made of a firstpower conductor C1, a second power conductor C2 and a common conductorCc.

As can be seen from these figures, the currents I1 s, I2 s, I1 c, I2 care defined as the currents flowing respectively on the first and secondpower conductors C1, C2 on the side of the source S and of the load C.And we define in the same way the voltages V1 s, V2 s, V1 c, V2 c thepotential differences present between the common conductor Cc and,respectively, the first and second power conductor C1, C2 on the side ofthe source S and of the load C.

Note that the voltages and currents referred to in the rest of thisdescription are by nature time-varying, i.e. they are expressed in theform V(t) and I(t). However, to simplify the writing, we will designatethese variable currents and voltages as V and I.

With reference to FIG. 3 , the network voltages on the side of thesource and of the load V_(net,s) V_(net,c) as the differential modevoltages present between the two power conductors C1, C2:V_(net,s)=V_(1s)−V_(2s) and V_(net,c)=V_(1c)−V_(2c). Similarly, wedefine the network currents on the side of the source and of the loadI_(net,s) I_(net,c) as the differential mode current flowing on the twopower conductors C1, C2: I_(net,s)=½*(I_(1s)−I_(2s)) andI_(net,c)=½*(I_(1c)−I_(2c)). Naturally, the network energy E_(net) overa determined observation period corresponds to the integral, over thisperiod, of the product I_(net)*V_(net). This network energy can beestablished on the side of the source E_(net,s) and of the loadE_(net,c)

When the section of the network in FIG. 3 is in normal operation andperfectly balanced, the network voltages V_(net,s), V_(net,c) and thenetwork currents I_(net,s), I_(net,c) on both sides of the line L areidentical. The network energies on the side of the source E_(net,s) andon the side of the load E_(net,c) are therefore also identical to eachother with the exception of the losses dissipated in the line.

The occurrence of a fault of the electrical network leads to itsunbalancing, and this unbalance can be made material by measuring theresidual voltages Vres,s, Vres,c which are defined on the side of thesource by the common mode voltage Vres,s=½*(V1 s+V2 s) and on the sideof the load by the common mode voltage Vres,c=½*(V1 c+V2 c). Similarly,we can measure the residual currents Ires,s Ires,c which are defined onthe side of the source by the common mode currents Ires,s=I1 s+I2 s andon the side of the load side by Ires,c=I1 c+I2 c. Naturally, theresidual energy Eres over a determined observation period corresponds tothe integral, over this period, of the product Ires*Vres. This residualenergy can be established on the side of the source Eres,s and of theload Eres,c.

Finally, we also define the mixed energy Emix over a determinedobservation period as the integral, over this period, of the productInet*Vres. This mixed energy can be established on the side of thesource Emix,s and of the load Emix,c.

As mentioned earlier, when the network in FIG. 3 is perfectly balanced,the residual voltages and currents are zero. The residual and mixedenergies on the side of the source Eres,s E_(mix,s) and on the side ofthe load E_(res,c) E_(mix,c) are also zero.

Parallel Type Fault Between the Power Conductors (Parallel Arc)

With reference to FIG. 4 a , a parallel type fault between the two powerconductors C1, C2 of the line of the network shown in FIG. 3 can bemodelled as a dipole DP1 placed between these two conductors C1, C2. Thedifference of the network voltages on the side of the source V_(net,s)and of the load V_(net,c) is not affected by the presence of thisdipole, but the circulation of a current in the dipole DP1 between thepower conductors C1, C2 leads to unbalance the network currentsI_(net,s) I_(net,c) on both sides of the line which are not identicalanymore.

In the event of such a parallel type fault between the two powerconductors C1, C2, there is no residual current or residual voltage.

A parallel type fault between the two power conductors C1 C2, such as aparallel arc, manifests itself as a difference in the currents I_(net,s)I_(net,c) and/or the network energies E_(net,s) E_(net,c) over thedetermined observation period, on both sides of the line. We note thatin the case of such a parallel arc, the energy dissipated in the dipoleDP1 which models it is much higher than the nominal power of thenetwork, so that the difference of the currents I_(net,s) I_(net,c)and/or of the network energies E_(net,s) E_(net,c) appearing on bothsides of the line allows to clearly detect this fault.

Practically, in the electrical network of FIG. 2 , the occurrence,during a period j, of a parallel type fault between two power conductorsC1, C2 connecting two detection devices D_(i), D_(i+1) of respectiveidentifier i and i+1 can be detected by the supervision device V, bycomparing to a threshold network energy value S_(i,i+1) the differenceof the network energies E^(j) _(net,i) E^(j) _(net,i+1), respectivelysupplied by means of the communication bus BUS by the detection devicesD_(i), D_(i+1). It is also possible to use a difference between thecurrents I^(j) _(net,i) and I^(j) _(net,i+1) supplied respectively bymeans of the communication bus BUS by the detection devices D_(i),D_(i+1) to detect and localize a parallel type defect. It can beprovided that the supervision device V may be configured to performother types of processing on the supplied network energies to detect theoccurrence of a fault of this type. For example, the energies suppliedduring several successive observation periods may be summed up before toproceed to the difference and the comparison with the threshold, inorder to extend the observation period. This allows to adapt the triggertimes according to the power of the fault: a very high-power fault willcause the supervision device V to react much faster than a lower powerdefect. This also allows to ensure that no protection is triggered if anon-persistent transient fault occurs.

Generally speaking, the trigger thresholds S_(i,i+1) associated with twodetectors of index i, i+1 are adapted according to the nature of theequipment E of the network 1 which can be localized between twodetection devices D_(i), D_(i+1) to take into account, for example,losses in lines or in connectors, or even the consumption of anequipment E of parallel nature and of known maximum power and lower thana characteristic power of fault.

Parallel Type Fault Between a Power Conductor and an Outer Element(Insulation Defect).

With reference to FIG. 4 b , a parallel type fault between one of thepower conductors C1, C2 and an element outside the network can bemodelled as a dipole DP2 placed between this conductor and this outerelement. The outer element can be the common conductor Cc, a mechanicalmass of the network, or any other potential.

The network voltages appearing on the side of the source V_(net,s) andof the load V_(net,c) are not necessarily affected by the occurrence ofsuch a fault, it depends on the scheme of connection to the groundretained for the network. There is almost no impact on the network,residual and mixed energies in case of a first fault of a regimereferred to as “IT regime”, i.e. when the network is isolated from theground or the mechanical mass. Nevertheless, to identify the occurrenceof this type of fault in this type of network, a permanent insulationcontroller can be exploited, as described in more detail below. On theother hand, significant differences in the network, residual or mixedenergies, will develop in the event of an insulation defect in anon-isolated network or in the event of a second fault in an isolatednetwork.

A current then flows in the dipole DP2 between the power conductor andthe outer element. Consequently, the current flowing on the side of thesource S and/or of the load C on this power conductor differs from thatflowing on the other conductor. This difference causes a residualcurrent on the side of the source Ires,s and/or on the side of the loadIres,c. The current flowing through the dipole DP2 develops a potentialdifference which also affects the voltage of the power conductor andgives rise to a residual voltage on the side Vres,s of the source or ofthe load Vres,c.

Consequently, the occurrence of an insulation defect gives rise to aresidual energy Eres,s or Eres,c on one side or the other of the lineover a determined observation period. In the event of a non-true defect,the residual energy variation will be more sensitive than the networkenergy variation.

By measuring, during a period of time j, in a measurement area of thenetwork and with the help of a detection device D of identifier iarranged in this area, the residual energy E^(j) _(res,i), it is thuspossible to detect the occurrence of such a fault, for example bycomparing the measured residual energy E^(j) _(res,i) with a determinedthreshold Si. This detection can be carried out locally, withoutnecessarily calling on the supervision device V of the network andwithout communicating the energy measurement to this device. Such alocal detection may allow to activate a local protection device P, inorder to isolate a portion of the network 1, as previously explained.

Such an insulation fault can lead to the occurrence of a residual energythat may be much lower than the nominal energy of the network. Inaddition, natural asymmetries can generate biases in the localcalculation of the residual energy (e.g. if the voltage of the commonconductor Cc is not exactly half the network voltage). The detection andthe localization of this fault is then facilitated by taking thedifference of these energies measured upstream and downstream of theline, using two detection devices D. The processing capacities of thesupervision device V, to which the residual energy measurements arecommunicated, are then exploited, as was presented in the previous case.

In other cases, the residual energy may be relatively small, and it maythen be advantageous to sum the residual energies measured over severalsuccessive observation periods before proceeding to the comparison withthe threshold, in order to extend this observation period.

In the case of an insulated network (regime IT type), which will be ableto continue to be fully operational in the event of a first insulationdefect, a permanent insulation controller (PIC) must be present todetect this first defect. This PIC measures the impedance between thenetwork and the mechanical mass or the ground and to do this, ittypically injects a common mode voltage (a residual voltage) into thenetwork at a very low frequency (typically 1 Hz). When the network ishealthy, there is no common mode current (residual current) andtherefore no residual energy. In the event of a first insulation defect,the PIC will cause the occurrence of residual currents and a residualenergy, in particular at the excitation frequency of the PIC. Thus, itis advantageous to measure a residual energy at the excitation frequencyof the PIC only in order to facilitate the localization of an insulationdefect. To do this, the PIC and the detection devices D must besynchronized, for example by sending a synchronization clock on thecommunication bus BUS.

Series Type Fault (Series Electrical Arc)

With reference to FIG. 4 c , a series type fault, such as a series arcoccurring on one of the lines L, most often on a connection terminal B,sometimes within the power conductors C1, C2, can be modelled as adipole DP3 placed in series on this conductor.

The currents of network on the side of the source Inet,s and on the sideof the load Inet,c are almost not affected by the presence of thisdipole DP3. But the flow of a current in this dipole DP3 gives rise to avoltage Vd which unbalances the voltage carried by this power conductor,while the other conductor is not affected. This dismetry gives rise to aresidual voltage on the side of the source Vres,s and/or on the side ofthe load Vres,c.

Consequently, the occurrence of a series defect gives rise, over adetermined observation period, to a mixed energy Emix,s or Emix,c on oneside and/or the other of the line. The series type defect also generatesa variation in network energy, but this is much lower than the nominalenergy and it will be impossible to detect the occurrence of a seriesdefect reliably and early via the analysis of the network energy. On theother hand, a series defect does not generate any variation in theresidual energy.

By measuring, during a period of time j, in a measurement area of thenetwork and with the help of a detection device D of identifier iarranged in this area, the mixed energy E^(j) _(mix,i) it is thuspossible to detect the occurrence of such a fault, for example bycomparing the measured energy E^(j) _(mix,i) with a determined thresholdSi. This detection can be carried out locally, without necessarilycalling on the supervision device V of the network and withoutcommunicating the measurement to this device. Such a local detection canallow to activate a local protection device P, in order to isolate aportion of the network, as previously explained. It is also possible touse a difference between the residual voltages V^(j) _(res,i) and V^(j)_(res,i+1) supplied respectively by means of the communication bus BUSby the detection devices D_(i), D_(i+1) to detect and localize a serialtype defect.

We note that the mixed energy E_(mix) is caused by the dissymmetrybetween the first and the second power conductor generated by thepresence of the series dipole DP3 which models a series type fault. Inorder to take full advantage of the detection capacity from the mixedenergy, we will therefore try to avoid intentionally making the powerconductors C1, C2 asymmetrical. For this reason, one of the two powerconductors should not be confused with the mechanical mass of thenetwork. It is also important to avoid inserting a connector or anyother element on only one of the power conductors in a line L.

In case of a “natural” dissymmetry of the network producing a mixedenergy in some measurement areas even in normal operation of thenetwork, this mixed balance energy can be determined and taken intoaccount for the detection of a fault, for example by adjusting the levelof the comparison threshold Si, or by identifying a temporal variationof the mixed energy. A calibration phase of the detection devices D ofthe network 1 (or of the supervision device V) can thus be provided,aiming at entering the level of the threshold value beyond which ameasurement of mixed energy or residual voltage testifies to theoccurrence of a fault of a serial type. Typically and as an example, aseries electrical arc produces a residual voltage between 20V and 50V.We can then choose the thresholds of detection of the difference of theresidual voltages towards 2V and, for the mixed energy, 2V thatmultiplies the value of the current In_(et). Thus, the detectionthreshold Si can advantageously be made to evolve according to theaverage value of the network current I_(net).

As in the 2 preceding types of faults, one can also supply themeasurement of mixed energy prepared by each of the detection devices Dto the supervision device V, which will then be able to detect morefinely and localize a series type defect by analysing the differences ofmixed energy between 2 detection devices D_(i) and D_(i)+₁. Successiveenergy measurements can also be processed, in sum or in difference, inparticular to allow the detection of the low power defects over a longerobservation period. The detection thresholds that apply respectively tothe measurements of network, residual and mixed energies, or to thedifferences in these energies between two devices, may be distinct fromeach other. It is specified that according to the conventions and thenature of the defect (for example a series arc on the first powerconductor C1 or a series arc on the second power conductor C2, thesethresholds can be negative and the notion of energy “higher” than athreshold is understood as absolute value.

To summarize this part of the description, we note that the measurementover a determined observation period and in a determined area of thenetwork, of the network energy E_(net), of the residual energy E_(res)and of the mixed energy E_(mix) allows to detect and localize theoccurrence of various faults. This detection can be carried out locallyin the measurement area by the simple observation of a network, residualor mixed energy exceeding a determined threshold. More accuratelocalization of these faults and the detection of a wider variety offaults may require exploiting the measurements of these energies betweentwo measurement areas of the electrical network 1.

In particular, it is possible to exploit the measurement of the mixedenergy at the level of a single measurement area to detect theoccurrence of a series-type fault, such as an electric arc in aconductor of a line of the network or of an equipment, for example asource, which was not easily possible with the techniques known in theprior art. This aspect is therefore an important advantage of thesolution described here.

To facilitate this detection, the lines L of the electrical network 1are advantageously designed to be as symmetrical as possible. In thisrespect, it is advantageous to choose the power conductors connectingthe electrical equipment E to each other so that they are identical orso that they have identical geometries (diameter and nature of theconductor and of the insulator). It can also be provided that the powerconductors and the common conductor are assembled parallel to each otherto form a cable harness, e.g. by means of cable ties, or even a singlecable, e.g. by embedding the conductors in an insulating material. Thislimits the asymmetries in the interaction of the conductors with theenvironment.

For the same reason of seeking balance, and in order to have zeroresidual voltages in the absence of defect, the common conductor can beconnected to a midpoint of the electrical equipment forming sources orloads. And we can equip the electrical equipment E forming sources orloads and not having a midpoint, a resistive bridge between the twopower conductors to connect the common conductor to the midpoint of thisresistive bridge.

In order to be able to elaborate a measurement of the network, residualand/or mixed energies, the fault detectors D are equipped with voltageand current sensors allowing to form an image of the voltages carried bythe conductors or flowing in the conductors to which they are connected,in the measurement area. Advantageously, these sensors have a goodlinearity, are slightly impacted by the environment (the temperature,the mechanical constraints, etc.) so as not to bias the energycalculations between two distant points of the network and are notexcessively sensitive to aging. They also have wide measurementpassbands, so that the measured energies take into account the spectraldisparity of the signals, voltages and currents of the network, inparticular during the occurrence of a fault.

Generally speaking, these sensors are adapted to elaborate a faithfulmeasurement in a frequency range between 0 Hz and 1 kHz, or even 10 kHzor 100 kHz, or even 1 MHz or 10 MHz or 100 MHz. The measuring membersO1, O2 may each comprise one or a plurality of such sensors. This caninclude in particular sensors working in different frequency ranges. Itcan thus be envisaged that a measuring member O1, O2 has a sensorallowing for measuring a direct component of a signal and/or a sensorallowing for measuring certain non-direct spectral components of asignal.

Advantageously, the sensors are adapted to supply measurements of adirect component of the current or of the voltage of the network 1,whether it is an AC or DC network, with a response time compatible witha required detection latency, for example less than or equal to onemillisecond. As a result, the measurement passband of these sensors istypically between 0 Hz and 1 kHz or several kHz. The measuring of theenergies from measurements taken in this frequency range is sufficientto detect most faults, in particular the series or parallel electricalarcs, with the required responsiveness.

In the case of an alternating AC network with active electricalequipment, sources or loads, the energies established from themeasurement of the direct components of the current and of the voltage,can testify to a fault in the operation of this equipment. The powertransformers can also be protected against the effects of the magneticsaturation induced by these direct components. In the case of analternating AC network with an IT-type (insulated) grounding scheme, themeasurement of the direct components will also allow to localize thefirst defect as mentioned above.

The sensors can also be adapted to supply an accurate measurement of thevoltages and of the currents in the frequency of the network to detectthe faults of overconsumption type or insulation defects. They can alsooperate beyond these frequencies in a very high frequency range beyond100 MHz. This is especially true for detecting partial discharge typedefects in insulators of the conductors of the network.

Detection Device

The principles underlying the invention having been stated, a detectiondevice D in accordance with the invention, and shown in FIG. 5 , is nowpresented in detail. As already stated with reference to the descriptionof FIG. 1 , such a detection device D is adapted to be connected to thepower conductors C1, C2 of the network 1 and to the common conductor Cc,and at the level of a measurement area of this network 1. These powerconductors can be those forming a line L of the network 1, or preferablythose internal to the electrical equipment E of the network. In such acase, the measuring members O1, O2 of a detection device D arepreferably placed upstream of the terminals B connecting a source to thedistribution lines L of the network and, preferably, downstream of theterminals B connecting a load to these lines L. In this way, it will bepossible to detect and localize a defect in these terminals B.

In its simplest version, the detection device D is designed to detect atleast the serial type faults, and is therefore configured to elaborate aquantity representative of a mixed energy which transits in themeasurement area and during a given observation period.

To this end, the detection device D comprises a first measuring memberO1, coupled to at least some of the conductors, allowing to elaborate afirst quantity Vres representative of the common mode voltage of thepower conductors C1, C2, i.e. the residual voltage. This first member O1can thus comprise sensors of the voltage present on each of the powerconductors C1, C2 with respect to the common conductor Cc. In a laterpart of this description, several preferred embodiments of this firstmember O1 will be given.

The detection device D also comprises a second measuring member O2,coupled to at least some of the conductors, and allowing to elaborate asecond quantity In_(et) representative of a network current. As anexample, this second member O2 may comprise a first current sensor formeasuring the current flowing on the first power conductor C1 and asecond current sensor for measuring the current flowing on the secondpower conductor C2, the difference of the measurements supplied by thesesensors being representative of the second quantity In_(et). In somecases, a single current sensor can be provided to measure, on only oneof these conductors, a quantity that is assimilated as a firstapproximation to the network current, and thus to the second quantitynet.

Advantageously, the current sensor or sensors of the second member areHall effect sensors, Neel Effect® sensors or sensors comprising aresistive shunt so as to draw a direct component of the measuredcurrents. It can be provided that the current sensor or the currentsensors of the second member comprise Rogowski type sensors or airtransformers. The extended passband, the linearity and the stability ofthese types of sensors can be used during the measurement of non-directspectral components. This is particularly true in the case of a researchof partial discharge type defect.

Whatever the nature of the components with which the first and secondmeasuring members O1, O2 are implemented, they allow to elaboratedirectly or indirectly (i.e. with the help of a calculator UP which willbe presented hereafter) a quantity Inet representative of the networkcurrent and a quantity Vres representative of the residual voltage.These two quantities allow to establish an image of the mixed energyE_(mix) which transits over a determined observation period, in themeasurement area of the detection device D defined by its position inthe network. To allow this, the detection device D also comprises acalculator UP, connected to the first and to the second measuring memberO1, O2. This calculator UP can take any suitable form, but it ispreferably a digital calculator having inputs allowing to digitize withhigh-frequency the analogue measurements supplied by the measuringmembers O1, O2. This calculator can be implemented by a microcontroller,a FPGA, a DSP, an ASIC or any other form of digital or analoguecalculation device that is suitable.

The detection device D may optionally comprise a converter CON, shown indotted line on FIG. 5 , adapted to draw energy from the power connectorsC1, C2 and/or from the common connector Cc to feed electrically thecalculator UP and all the other active elements that make up the deviceD, it being understood that the power required is particularly reduced.When designed to be connected to a communication bus BUS, as shown inrelation to FIG. 1 , the detection device D can alternatively be fed bya dedicated port of this bus.

For completeness, but not as an essential characteristic, the detectiondevice may also comprise a network controller NET, which may beimplemented by the calculator UP, and allowing to interface the device Dwith the communication bus BUS. The device D is associated with anidentifier, such as a network address, which allows it to be identifiedon the network. The bus BUS allows to communicate a clock information tothe calculator UP, or the device D can have a dedicated clock terminalallowing to receive this information. In this way, the calculator UP cantime-stamp the data it elaborates before placing them on thecommunication bus BUS. In this way, the supervision device V, to whichseveral detection devices D similar to the one shown in FIG. 5 areconnected as we have already seen, can order the data received fromthese devices D and exploit them in a temporally coherent sequence.

The calculator UP of the detection device D is configured by hardware orby software to make the acquisition of the measurements supplied by thefirst and the second measuring member O1, O2, and to determine an imageof the mixed energy E^(j) _(mix) which transits, during a given periodof time j, in the measurement area. The frequency of acquisition of themeasurements by the calculator is typically less than a millisecond, forexample it can be of the order of 100 microseconds or 10 microseconds,or even 100 ns or less depending on the passband of the measuringmembers O1, O2. The observation period can be between 100 ns and 10 s.It is specified that the calculator UP can be configured to digitallyprocess the measurements supplied by the measuring members O1, O2 or beconfigured to combine a plurality of measurements supplied by each ofthese members O1, O2 to determine the image of the mixed energy E^(j)_(mix). For example, the calculator can be configured to integrate ameasurement supplied when a sensor of a member O1, O2 delivers aninformation proportional to the time derivative. It can be configured toadd a direct current/voltage measurement and a variation measurement ofthis current/voltage (after its integration), when these twomeasurements are supplied separately for one of the two measuringmembers O1 and/or O2.

The calculator UP may also be configured to exploit the determined mixedenergy Ejmix so as to detect a series-type fault in the network, asdiscussed in an earlier section of this description. In particular, itcan be determined whether this determined mixed energy Ejmix, or avariation of this energy between two distinct observation periods,exceeds a predetermined threshold. As we have also seen, the calculatorcan be configured to sum the determined mixed energies Ejmix, Ej+1mix .. . , Ej+nmix over consecutive observation periods j, j+1, . . . , j+n.The accumulated mixed energy is then compared to a threshold so as todetermine the occurrence of a fault.

When such a fault is confirmed, and regardless of the way in which thecalculator exploits the mixed energy measurement or measurements Ejmix,the calculator UP can generate a signal S indicating this fault, thesignal being able to be transferred to a detection terminal of thedevice D. In such a case of use of the detection device D, it isunderstood that the presence of the communication bus BUS is notnecessary. Alternatively, the signal S can be placed on thecommunication bus BUS. Alternatively, the calculator UP can simplyelaborate by calculation the data representative of the mixed energyEjmix and place this data on the communication bus BUS. In this lastalternative, the detection of a fault in the network is entirelyimplemented by the supervision device V as previously presented.

In a more complete embodiment of the detection device D, the latter maycomprise other measuring members or more complete first and secondmeasuring members O1, O2 allowing the calculator UP to determine, inaddition to the image of the mixed energy E^(j) _(mix), the image of thenetwork energy E^(j) _(net) and of the residual energy E^(j) _(res)which transit in the measurement area during the determined observationperiod j. In addition to the second quantity I_(net) representative ofthe network current and the first quantity V_(res) representative of theresidual voltage, these members allow to establish a third quantityV_(net) representative of the network voltage and a fourth quantityI_(res) representative of the residual current. This more completeembodiment is symbolized by the dotted arrows V_(net) and I_(res) inFIG. 5 .

Detection Device Integrated into an Active Equipment

A detection device D can be integrated into an electrical equipment Ecomprising a load or an active source, for example an inverter, or agenerator whose correct operation is to be monitored. In this case, andin order to be able to detect a series arc, the detection device D willbe positioned as close as possible to the active portion of theequipment E, i.e. just before the power switches, and downstream of theconnection terminals B of this equipment and downstream of a possibleprotection device P when this equipment E is a load. Preferably, aresistive dividing bridge is placed between the power conductors C1, C2,the midpoint of which is connected to the common conductor closest tothe active load. It will be possible to measure a mixed energy, image ofthe presence of a defect in series in the internal conductors of themonitored equipment E.

In the same way that we tried to distinguish the energies in thenetwork, we can try to distinguish the energies consumed by a load. Forthis, we can define 4 types of energy:

-   -   An energy referred to as “useful energy”, characterised by        current-voltage spectra at the frequency of the network, between        0 and 10 Hz for a direct DC network or at +/−5 Hz of the network        frequency for an alternating AC network.    -   A harmonic distortion energy, characterised by current-voltage        spectra in a band of +/−5 Hz around multiples of the network        frequency (for an alternating network). This energy is        essentially reactive.    -   A switching energy, characterised by current-voltage spectra at        frequencies multiple of a chopping frequency FHACH of the active        load. This energy is limited to bands of +/−5 Hz around these        multiple frequencies n*FHACH.    -   An additional energy that is not in any of the above bands. A        priori, only noise or energy is found in this band in the event        of electric arc (series or parallel) or short-circuit.

A detection device D integrated in the equipment E will establish thenetwork E_(net), residual E_(res) and mixed E_(mix) energies aspresented in the previous sections of this description in order, forexample, to transmit this information to the supervision device V. Inaddition, the detection device D will be able to establish adecomposition of these energies according to the four aforementionedcategories in order to identify the contributors. For this purpose, thedetection device D can apply a filtering on the quantities supplied bythe measuring members O1, O2 in order to separate these quantitiesaccording to the various spectral bands described, before proceeding tothe calculation of the energies in each of these bands with the help ofthe calculator UP.

This filtering can implement comb filters implemented by the calculatorUP, in order to be able to enslave in particular the frequency of thecomb with the chopping frequency. For this purpose, it can be providedthat this chopping frequency is supplied in the form of a chopping clockFHACH resulting from the active load and presented on a dedicatedconnection terminal of the detection device (shown in FIG. 5 ).

Thus, we can establish by means of the calculator UP:

-   -   a network energy “useful E_(net)” as the useful energy in the        load or the source. This energy may reveal an overload or a        parallel arc.    -   A network energy “switching E_(net)” as the energy lost in the        switching structures of the electrical equipment E. This energy        may reveal a switching fault, such as a short-circuit in the arm        (not respecting dead times) or a switch fatigue.    -   A network energy “additional E_(net)” as being the additional        energy, for example due to a parallel or series arc or a        short-circuit.    -   A mixed energy “Switching E_(mix)” representative of a switching        fault in a more refined way than the mixed energy E_(mix) alone.        In particular, the presence of a series arc in the equipment E        can be identified by eliminating the switching mixed energy from        the mixed energy E_(mix).

These energies can be placed on the communication bus BUS andtransmitted to the supervision device V in order to be exploited.

Preferred Embodiment of the First Measuring Member

To ensure a detection and a localization of faults, and in particular ofa series arc in an alternating or direct network, it may be sufficient,as we have seen, to measure the direct components of a residual voltageV_(res) and of a network current I_(Net). These measurements are carriedout by respectively the first and the second measuring member O1, O2 ofthe detection device D.

For the measurement of the direct component of the common mode voltage,i.e. the residual voltage V_(res), the first measuring member O1 can beequipped with a resistive voltage dividing bridge, a first electrode T1of the bridge being electrically connected to the first power conductorC1, a second electrode T2 being electrically connected to the secondpower conductor C2, and a third electrode T3 being electricallyconnected to the midpoint of the bridge. The voltage developing betweenthis midpoint, on the third electrode T3, and the common conductor CCvia a measuring dipole SH supplies the common mode voltage. Typically,this dipole is formed by a resistor. A schematic diagram of such abridge is shown in FIG. 10 in which the resistors R1, R2 forming thebridge are precisely chosen to have the same value, to within 1%, oreven to within 0.1% or even 0.01%, and limiting their drift in time andtemperature to a minimum. In such a scheme, the quantity representativeof the common mode voltage V_(res) is equal to the common mode voltagepresent on the two power conductors multiplied by a gain equal toSH/[R1/2+SH]. This gain allows to reduce the dynamic range of themeasurement in order to adapt it to that of the electronics of themeasuring member. As an illustration, by choosing R1=1 MOhms, and SH=50kOhms, a gain of 1/11 allows to reduce a common mode voltage of 50V onthe power conductors to a quantity V_(res) representative of the orderof 5V so that it can be processed by the rest of the electronics of themeasuring member. The values of the resistors R1, R2 and SH should bechosen in order to adapt to the quantities of the network and to thedynamics of the measurement electronics.

As already mentioned, the detection device D is equipped with connectionterminals B intended to associate the device with the conductors C1, C2,CC. These terminals B are therefore also electrically connected to theelectrodes of the resistive bridge.

For example, the resistive dividing bridge can be composed of a thinlayer (or thin film) or thick layer (or thick film) resistor allowing toensure an adequate voltage withstand and control the transformationratio without thermal or time drift. To ensure a perfect symmetrybetween the two resistive elements R1, R2, and thus reduce the driftsover time and as a function of the temperature, a resistive dividerreferred to as a “3-terminal units” divider is used to form theseresistive elements.

When it is chosen to measure non-direct components of the residualvoltage, it is preferable that the sensor allowing this measurement isinsensitive to a possible direct component, is perfectly linear, thatits gain is controlled and does not drift either in temperature or intime. This is especially true for a partial discharge type defectdetection. To this end, and in a preferred embodiment, a schematicdiagram of which is shown in FIG. 6 , it is proposed to use twocapacitive elements EC1, EC2 arranged in a bridge between the two powerconductors C1, C2, having substantially identical capacitance values towithin 1%, or even 0.1%, or even 0.01%. These elements are respectivelyeach connected at a midpoint M. The midpoint M is electrically connectedto the common conductor Cc via a measuring dipole SH of the common modevoltage.

The currents I1, I2 flowing in the capacitive elements EC1, EC2 arerespectively proportional to the derivatives, as a function of time, ofthe potentials V_(c1), V_(c2) carried by the power conductors C1, C2.The capacitance values of the capacitive elements EC1, EC2 beingidentical, the differential current I1-I2 is proportional to thederivative of V_(c1)+V_(c2), i.e. the common mode voltage V_(res). Thus,it is sufficient to measure this differential current I1-I2 for exampleby means of a current sensor arranged in a branch of the circuitconnecting the midpoint M between the capacitive elements and the commonconductor Cc, then to integrate it as a function of time in order toobtain the residual voltage V_(res). To this end, the measuring dipoleSH placed between the midpoint M and the common conductor Cc is part ofthe current sensor and has a low impedance of less than 1 kOhm or evenless than 1 Ohm. The integration is not necessarily carried outanalogically in the first measuring member itself as symbolized in FIG.6 , and the calculator UP can be configured to perform this operation.

Alternatively, non-direct components of the common mode voltage V_(res)between the midpoint M and the common conductor Cc can be measureddirectly by choosing a high impedance of the measuring dipole SH,greater than 1 kOhm, or even greater than 1 MOhm. The member O1 thencomprises a capacitive divider delivering the residual voltage withrespect to the common conductor Cc. This second solution is however lesssuitable for severe electromagnetic environments (such as in anaircraft), but may be suitable in a photovoltaic farm as a complement tothe direct components.

To ensure a perfect symmetry between the two capacitive elements EC1,EC2, and thus reduce the drifts in time and temperature, a capacitorreferred to as “3 terminal unit capacitor” is used to form thesecapacitive elements.

Such capacitors comprise electrodes of type A, type B and type G (FIG. 7), each type being electrically associated with a terminal unit, andstacked on top of each other and insulated from each other by adielectric, and following an alternation A, G, B, G, A, G, B, etc. Theelectrode G of the capacitor is directly the midpoint M, which isconnected to the common conductor Cc via the measuring dipole SH, andthe electrodes of types A and B are respectively connected to the powerconductors C1, C2 by means of the three terminal units of thecapacitator. The advantage of this structure is to obtain almostidentical capacitive elements EC1, EC2, invariant in time and stable intemperature between the terminal unit of type G and the terminal unit oftype A on the one hand, and between the terminal unit of type G and theterminal unit of type B on the other hand. The three terminal unitscapacitors also have a very low parasitic inductance, which allows toproceed to measurements at very high frequencies.

The dielectric of the capacitor can be of the COG or NPO type. It isalso possible to use a paper-based dielectric, possibly filled with oil,or with mica or other insulators, allowing to obtain an excellentbehaviour in high frequencies, stable in time, for medium or very highvoltages.

The capacitor may be a film capacitor, in which each type of conductorand the dielectric are in the form of a film, and are stacked on top ofeach other. The stack can be rolled up to form a cylindrical orparallelepiped three-terminal unit capacity.

Of course, these concepts can be extended to form capacities with morethan three terminal units, which can be useful when the network isthree-phase for example.

Advantageously, it can be provided that the first measuring member O1also allow to establish the network voltage Vnet, i.e. the differentialmode voltage, in addition to the residual voltage Vres, i.e. the commonmode voltage. For example, a resistive and/or capacitive voltage dividercan be used depending on the nature of the spectral components of thenetwork voltage Vnet that we wish to measure.

FIG. 11 shows a resistive dividing bridge with 4 resistors R1, R1′, R2,R2′ and 5 electrodes T1 to T5. We find the 2 electrodes T1, T2 allowingto connect the bridge to the conductors C1, C2, the third electrode T3allowing to draw and measure a midpoint voltage corresponding to thecommon mode voltage between the two power conductors. The seriesresistance R1+R1′ formed by the resistors R1, R1 arranged on one side ofthe midpoint is therefore equal to the series resistance R2+R2′ formedby the resistors R2, R2′ arranged on the other side of the bridgerelative to the midpoint. Complementary electrodes T4, T5 arranged atthe level of the intermediate points of series connection of theresistors in each branch of the bridge, allowing to supply a voltageimage of the network voltage V_(net) by means of a control gain (definedby the relation (R1+R1′)/(R1+R1′+R2′+R2)). The voltage drawn off betweenthe complementary electrodes T4, T5 is thus compatible with the rest ofthe processing operated by the electronic acquisition chain. Forexample, if the network voltage V_(net) is about 800V, we can choose theresistors of the bridge so that the gain is about 1/100.

For example, the two resistive elements R1, R2 can be chosen to be equalto each other, for example between 10 kOhms and 1 MOhms, and equal to 99times the first resistor R1′ connected to the midpoint T3. The otherresistor R′2 connected to the midpoint, on the other side of this point,is also chosen so that it has the same value as the first resistor R1.The control gain applied to the differential mode voltage presentbetween the two power conductors, equal to (R1+R1′)/(R1+R1′+R2′+R2), isthen equal in this case to R′1/(R1+R′1).

Thus, and in a preferential way, the resistive bridge is implemented bya single component of the paired resistive divider type, i.e. in whichthe value of certain resistors is fixed in advance according to apredetermined ratio with respect to the other resistors, and in whichall the resistors are carried out on a same support (“thick film” or“thin film”) in order to reduce the thermal drifts. The result is aresistive divider with 3 terminal units or 5 terminal units, dependingon the chosen embodiment.

In the case of the measurement of non-direct components, and in order toimprove the performance in harsh environment, it is sufficient torealize that the common mode current I1+I2 flowing in the two capacitiveelements EC1, EC2 of the capacitive divider shown in FIG. 6 forms animage of the derivative as a function of time of the differential modevoltage V_(net). By equipping the first member O1 of a common modecurrent sensor, it is possible to establish this differential modevoltage V_(net). This common mode current sensor can be formed by twoair coils, for example two Rogowski probes, respectively arranged in thevicinity of the capacitive elements EC1, EC2.

An example of the implementation of these principles is then shown inFIG. 7 . A cylindrical three-terminal unit capacitor has been formedfrom films of type A, B, G wound as previously described, and whosethree terminal units T1, T2, T3 are electrically connected to the firstpower conductor C1, the common conductor via the dipole SH and thesecond power conductor C2, respectively. The resistance of the measuringdipole SH between the terminal unit T2 (forming the midpoint M betweenthe two capacitive elements EC1, EC2 in the capacitor) and the commonconductor C allows the extraction of a quantity representative of thecommon mode voltage Vres, as previously described. Two Rogowski typecurrent sensors RG1, RG2 are arranged in a winding around thecylindrical capacitor in order to draw an image of the currents I1, I2flowing in the capacitor. The quantities supplied by these sensors canbe combined to give an image of the differential mode voltage Vnet.

In an advantageous embodiment, the current sensors allowing to elaborateimages of the differential mode voltage V_(net) and/or the common modevoltage V_(res) implement a planar coil technology. In this case, twotypes of coils arranged in parallel but distinct planes can be realized,which allow to measure respectively the common mode current (image ofthe derivative of the differential mode voltage V_(net)) and thedifferential mode current (image of the derivative of the common modevoltage V_(res)). These two planes can be localized in different layersof a multilayer printed circuit board in which the planar coils havebeen localized.

As shown in FIGS. 8 a, 8 b , this printed circuit board can comprise, ona first layer, two tracks P1, P2 respectively electrically connected tothe power conductors C1, C2. These tracks are also connected to thethree-terminal unit capacitor C3, whose midpoint M is electricallyconnected to the common conductor Cc via a measuring dipole SH, formedhere by a single conductor, in order to form the differential current.The planar coils for measuring the differential current Bcd, for examplefour of these coils formed by two pairs of coils mounted in anti-serial(FIG. 8 a ), can be placed on a second layer of the board and the planarcoils for measuring the common current Bcc, which can also be four, canbe placed on a third layer of the board (FIG. 8 b ).

This variant is advantageous in that it allows to eliminate theinfluence of a current flowing in the common conductor, regardless ofits frequency. The planar coils deliver an electromotive forceproportional to the second derivative of the measured voltage withrespect to time, which must therefore be integrated twice beforeproceeding with the calculation of the energies. This assembly ispreferably carried out according to a printed circuit board technologyfor the power applications in order to control the geometry of the coilsand to obtain a known transformation ratio without calibration and withan extremely low drift in temperature and time. Note that this approach,in general, can be implemented to measure the differential mode voltageV_(net) or the common mode voltage V_(res).

Generally speaking, the measuring member O1 can be equipped with sensorsfor the direct component and the variable component of the common modevoltage Vres. It can also be equipped with sensors for the directcomponent and the variable component of the differential mode voltageVnet.

Of course, the invention is not limited to the described embodiments andalternative embodiments may be made without departing from the scope ofthe invention as defined by the claims.

Thus, a device D in accordance with the invention provides for theelaboration of a quantity representative of the mixed energy E_(mix)from the common mode voltage and the network current and which transitsin the measurement area. This quantity is processed and compared to athreshold to identify a fault. It is perfectly understandable that thequantity representative of the mixed energy can correspond to the commonmode voltage which is compared to a threshold modulated according to theintensity of the network current. In all cases, the first and the secondquantity that make up the mixed energy E_(mix) are exploited to generatea signal S indicating the fault of the network. It is therefore notnecessary for a detection method in accordance with the invention toimplement a formal energy calculation, although this makes a particularembodiment.

The invention claimed is:
 1. A member for measuring a quantityrepresentative of a common mode voltage (V_(res)) in an electricalnetwork or in an equipment, the network or the equipment comprising atleast a first power conductor and a second power conductor, themeasuring member comprising two capacitive elements which are intendedto be arranged in a bridge between the two power conductors and having acapacitance values that are identical to each other, the two capacitiveelements being connected at a midpoint, the measuring member furthercomprising a measuring dipole connected on the one hand to the midpointand on the other hand to a connection terminal intended to beelectrically connected to a common conductor of which the electricalnetwork or the equipment has been equipped.
 2. The measuring memberaccording to claim 1 wherein the measuring dipole has an impedance ofless than 1 kOhms, the dipole being able to develop a voltageproportional to the derivative with respect to time of a common modevoltage (V_(res)) present between the two power conductors.
 3. Themeasuring member according to claim 1 wherein the measuring dipole hasan impedance greater than 1 kOhms, the dipole developing a voltageproportional to a common mode voltage (V_(res)) present between the twopower conductors.
 4. The measuring member according to claim 1 whereinthe capacitive elements are formed by a three-terminal capacitor, afirst terminal being intended to be electrically connected to one of thepower conductors, a second terminal being intended to be electricallyconnected to the other of the power conductors and the third terminalbeing intended to be connected to the common conductor.
 5. The measuringmember according to claim 4 wherein the three terminal capacitor is madefrom only 3 electrodes.
 6. The measuring member according to claim 4wherein the three-terminal capacitor is made with sheets stacked andthen rolled up to form a cylinder or a 3-terminal parallelepiped.
 7. Themeasuring member according to claim 1, further comprising athree-electrode resistor having a midpoint, the first electrode beingintended to be electrically connected to the first power conductor, thesecond electrode being intended to be electrically connected to thesecond power conductor, the common mode voltage (V_(res)) being presentbetween the midpoint of the three-electrode resistor and the commonconductor.
 8. The measuring member according to claim 1 comprising acurrent sensor, capable of measuring the differential mode currentflowing in the two capacitive elements, in order to establish a quantityrepresentative of the common mode voltage (V_(res)), and formed of atleast four air coils respectively arranged in the vicinity of thecapacitive elements.
 9. The measuring member according to claim 1,further comprising a current sensor, capable of measuring the commonmode current flowing in the two capacitive elements in order toestablish a quantity representative of a differential mode voltage(V_(net)).
 10. The measuring member according to claim 9 wherein thecurrent sensor capable of measuring the common mode current is formed byat least two air coils respectively arranged in the vicinity of thecapacitive elements.
 11. The measuring member according to claim 1further comprising a sensor of the DC component of the common modevoltage (V_(res)).
 12. The measuring member according to claim 1 furthercomprising a sensor of the DC component of the differential mode voltage(V_(net)).
 13. A device for detecting a fault in an electrical network,the electrical network comprising at least one electrical equipmentelectrically connected to a first power conductor and to a second powerconductor, the network also being provided with a common conductor, thedevice being intended to be connected to the power conductors and to thecommon conductor at a measurement area and comprising: a first measuringmember in accordance to claim 1; a second measuring member for producinga second quantity (I_(net)) representative of a network current flowingthrough the power conductors; a calculator, connected to the first andsecond measuring members, the calculator being configured to determine,over a determined observation period, a quantity representative of aso-called “mixed” energy (E_(mix)) defined as the integral over thedetermined observation period of the product of the common mode voltageand the network current and conveyed in the measurement area, thequantity representative of the mixed energy (E_(mix)) being determinedfrom the first quantity (V_(res)) and from the second quantity(I_(net)).
 14. The detection device according to claim 13 wherein thesecond measuring member comprises an air coil, for example of theRogowski type.
 15. The detection device according to claim 14 whereinthe second measuring member also comprises a direct current sensor, forexample a Neel Effect® sensor.